1. Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular, to a hot runner nozzle with a variable length in operation.
2. Related Art
In a multi-cavity injection molding apparatus having a manifold for delivering a melt stream of moldable material to a plurality of nozzles, the heat distribution throughout the manifold is typically uneven. This uneven heat distribution causes the manifold to deflect. As a result, the distance between the lower surface of the manifold and each of a plurality of mold cavities varies and thus each nozzle is subjected to unique operating conditions depending on the nozzle location relative to the manifold. The nozzles also experience thermal expansion, however, the nozzles are generally fixed between the mold cavities and the manifold. As such, the thermal expansion results in a variable sealing force being applied to both the manifold and the mold gate which is not desirable since it will allow the pressurized melt to leak at the interface between the manifold and each nozzle, as well as at each gate around the nozzle seals if the manifold floats and is retained by only the head portion of each injection nozzle. Such leakage may also occur in nozzles threaded into the manifold, but only at the gate area.
What is needed is a hot runner nozzle that accommodates thermal expansion of a nozzle without causing a variable force to be applied between the nozzle and a manifold or a mold gate of an injection molding apparatus.